A ultraviolet (UV) imprint method attracts attention as a fine processing method for effectively producing, at low cost, electronic devices such as a large-scale integrated circuit, a liquid crystal display, and the like, a patterned media, a microchannel device, a biochip, and the like.
The UV imprint method includes transferring a pattern to a substrate by etching using a pattern formed by molding a resist film as a mold. In this method, the resist film having a pattern formed therein is required to have high etching resistance. Known examples of the UV imprint method include a method of directly transferring a pattern to a substrate, a bilayer resist method using a resist film as a first resist layer and a substrate having a second resist layer and an underlayer substrate, and the like. A known example of the bilayer resist layer is a method using a silicon-containing resin for the first resist layer and including transferring a pattern to the second resist layer by etching with oxygen-based gas plasma and transferring the pattern to the underlayer substrate by further etching the second resist layer to which the pattern has been transferred.
A quartz mold is normally used as the mold used in the UV imprint method. The quartz mold satisfactorily transmits UV light and has high hardness and high surface smoothness, and is thus a material suitable for the UV imprint method. However, quartz is difficult to process and thus the quartz mold is more expensive than other mold materials. In addition, the mold is repeatedly used, and the presence of residues on the mold influences pattern formation, thereby causing the need for complete washing. However, the UV imprint method, particularly a nanoimprint method for an ultrafine pattern, has the problem of clogging a mold pattern with a resist cured product.
Therefore, a method of plasma ashing the quartz mold with oxygen gas is used for removing the residues on the mold. However, when a resist resin is a silicon-containing resist, SiO2 is produced by plasma treatment, and there is thus the problem that the residues cannot be removed by plasma ashing treatment.
Also, Patent Literature 1 discloses a method for removing mold residues by using, as a resist, a resin which is solubilized by acid treatment. However, the resin used has low resistance to dry etching with oxygen-based gas because it does not contain silicon and has a low concentration of curable functional groups, thereby causing the possibility of decreasing the precision of pattern transfer to a substrate.